Clark is notorious for taxi rip-off prices ...like p500 just to basically get you off the airport perimeter. There's a proper little taxi mafia there from what I've heard, so be prepared to negotiate hard, and certainly discuss your options with any more-experienced fellow travellers on the plane before you go into battle.
I have never done the route you're planning, so I'm afraid you're likely to be stuck with a taxi all the way. Just try to keep the price down to merely extortionate.
Me, I'd just get Jeepney to Dau and another Jeepney/minibus/public bus like Victory liner to Manila (which stops at San Fernando) from there to San Fernando.
A lot depends on the time of day of course.
